System for increasing RF power as a constant over a temperature range and employing reduced transmitter current drain during low power output periods

ABSTRACT

A system and method for transmitting data communications through air using a radio. The invention allows the user to select from a number of predetermined output transmission powers. When a lower output transmission power is selected the current drain to the associated amplifier is decreased thereby conserving battery power of the radio. In addition, a detector diode circuit combined with an adjustable gain amplifier combine to provide a feedback mechanism whereby the output transmission power of the radio is held substantially constant over a broad range of temperatures.

FIELD OF INVENTION

The present invention relates generally to a power amplifier circuit foruse in radios directed towards the transmission of wireless datacommunications. The invention is directed to the wireless local areanetwork environment. More particularly, the present invention isdirected towards a system for selectably increasing the transmissionpower of radios used in wireless computer networks over a broad range oftemperatures and reducing the current drain as the transmit power of theradio is decreased so as to extend the battery life of such a device.

BACKGROUND OF THE INVENTION

The use of wireless networks has increased dramatically over the pastfew years. Wireless local area networks (“WLANs”) are now commonplace inthe small office/home office (“SOHO”) environment as well as thecommercial building to commercial building environment. A WLAN offersseveral advantages over regular wired local area networks (“LANs”). Forexample, users are not confined to specified locations previously wiredfor network access, wireless work stations are relatively easy to linkwith an existing LAN without the expense of additional cabling ortechnical support; and WLANs provide excellent alternatives for mobileor temporary working environments.

In general there are two types of WLANs, independent and infrastructureWLANs. The independent, or peer-to-peer, WLAN is the simplestconfiguration and connects a set of personal computers with wirelessadapters. Any time two or more wireless adapters are within range ofeach other, they can set up an independent network. In infrastructureWLANs, multiple base stations link the WLAN to the wired network andallow users to efficiently share network resources. The base stationsnot only provide communication with the wired network, but also mediatewireless network traffic in the immediate neighborhood. Both of thesenetwork types are discussed extensively in the IEEE 802.11 standard forWLANs.

In the majority of applications, WLANs are of the infrastructure type.That is, the WLAN typically includes a number of fixed base stations,also known as access points, interconnected by a cable medium to form ahardwired network. The hardwired network is often referred to as asystem backbone and may include many distinct types of nodes, such as,host computers, mass storage media, and communications ports. Alsoincluded in the typical WLAN are intermediate base stations which arenot directly connected to the hardwired network.

These intermediate base stations, often referred to as wireless basestations, increase the area within which base stations connected to thehardwired network can communicate with mobile terminals. Associated witheach base station is a geographical cell. A cell is a geographic area inwhich a base station has sufficient signal strength to transmit data toand receive data from a mobile terminal with an acceptable error rate.Unless otherwise indicated, the term base station will hereinafter referto both base stations hardwired to the network and wireless basestations. Typically, the base station connects to the wired network froma fixed location using standard Ethernet cable, although in some casethe base station may function as a repeater and have no direct link tothe cable medium. Minimally, the base station receives, buffers, andtransmits data between the WLAN and the wired network infrastructure. Asingle base station can support a small group of users and can functionwithin a predetermined range.

In general, end users access the WLAN through WLAN adapters, which arecommonly implemented as PCMCIA cards in notebook computers, ISA or PCIcards in desktop computers, or fully integrated devices within hand-heldcomputers. WLAN adapters provide an interface between the client networkoperating system and the airwaves. The nature of the wireless connectionis transparent to the network operating system.

In general operation, when a mobile terminal is powered up, it“associates” with a base station through which the mobile terminal canmaintain wireless communication with the network. In order to associate,the mobile terminal must be within the cell range of the base stationand the base station must likewise be situated within the effectiverange of the mobile terminal. Upon association, the mobile unit iseffectively linked to the entire LAN via the base station. As thelocation of the mobile terminal changes, the base station with which themobile terminal was originally associated may fall outside the range ofthe mobile terminal. Therefore, the mobile terminal may “de-associate”with the base station it was originally associated to and associate withanother base station which is within its communication range.Accordingly, WLAN topologies must allow the cells for a given basestation to overlap geographically with cells from other base stations toallow seamless transition from one base station to another. One exampleof this “association” process is described extensively in IEEE 802.11.

The radio component of WLAN adapters receive and transmit data via radiofrequency (“RF”) or infrared (“IR”) media. Currently, it is common formanufacturers of WLAN devices to utilize integrated chip sets from thirdparty developers. In the WLAN field, one such manufacturer is Intersilwhich manufactures and sells the PRISM I® and the PRISM II® chip set.The PRISM I® chip set is a first generation chip set which providedrudimentary functions to the WLAN developer. However, the PRISM I® chipset did not perform as well in a confined, multi-path environment as itperformed outdoors in a single path environment. The PRISM II® chip setis a second generation chip set which is highly integrated. The PRISMII® chip set also has more signal processing capabilities for betterperformance in a multi-path environment. Since the PRISM II® chip set ishighly integrated, the developer must abide by design trade-offs made bythe manufacturer. One such design trade-off limits the transmit power ofthe radio and therefore limits the range of communication associatedwith devices incorporating the chip set.

While it is possible to increase the output power of the integrated chipset various problems arise that will affect the transmitted signal.Normally, this is observed in the transmit spectrum mask. FIG. 1illustrates the mandated transmit spectrum mask associated with IEEEstandard 802.11. As shown, a conforming device must a have transmitspectral mask of less than −30 dB at the channel center frequency ±11-22MHz and −50 dB for the channel center frequency ±22-33 MHz. Generally, aproblem arises when the developer attempts to increase the transmitpower for the integrated chip set beyond that set by the manufacturer.Upon such increase in the transmit power, a device previously conformingto the transmit spectral mask no longer meets the requirements andbecomes non-conforming, that is the signal does not achieve the mandated−30 dB decrease at ±11-22 MHz from channel center frequency or the −50dB decrease from the channel center frequency at ±22-33 MHz.

Another problem encountered with current wireless LAN chip sets is thatthey typically have a transmit power amplifier with a relatively lowcompression point and a fixed current bias setting. This results inlimited transmit output power, in the Intersil PRISM II® chip set, theoutput transmit power is typically around 30 mW. In addition, whilelower output power levels such as 15 mW and 1 mW are possible bydecreasing the transmit gain of the I/Q modulator chip, the transmitpower amplifier's current drain at the 15 mW and 1 mW output levels isthe same as the current drain at the 30 mW output level. Thus, batterylife may be extended by lowering the transmit current drain whenoperating at lower power levels.

The present invention addresses these and other problems encountered inthe prior art, to provide a system for increased output transmitterpower effective over a broad range of temperatures.

SUMMARY OF THE INVENTION

According to the present invention there is provided a system forincreasing the transmit output power of a radio used in wireless datacommunications, thereby effectively increasing the communication rangeof such devices. The present invention also reduces the transmit currentdrain of the power amplifier when the radio is operating at less thanits maximum output range, thereby conserving battery life of the radio.The system comprises: an apparatus for transmitting data communicationsthrough air using a radio comprising: a receive means adapted forreceiving an associated data input signal; a modulating means adaptedfor modulating the associated data input signal; a spreading means forperforming a direct sequence spread spectrum operation on the associateddata input signal resulting in a spread data input signal; a convertingmeans for converting the spread data input signal to a spread radiofrequency data signal; an amplifier means for amplifying the spreadradio frequency data signal with a first amplifier having an adjustablegain control; an amplifying means for amplifying the spread radiofrequency data signal with a second amplifier having an adjustable biascurrent control for selecting a bias current for a desired transmissionoutput power wherein selection of a lower transmission power results ina lower current drain; a detecting means for detecting a power signalcreated from at least a portion of the radio frequency data signal; aprinted circuit board coupler that couples transmission power to a radiofrequency detector diode circuit; a digital to analog converter forconverting the at least a portion of the radio frequency data signal toan analog error signal; an amplifying means for amplifying the radiofrequency data signal proportionately with the error signal by adjustingthe gain control of the first amplifier to achieve a substantiallyconstant output transmission power over a selected temperature range;and transmission means adapted for transmitting the radio frequency datasignal through at least one associated antenna.

According to another aspect of the invention there is provided a methodfor increasing the transmit output power of a radio used in wirelessdata communications, thereby effectively increasing the communicationrange of such devices. The method comprises: receiving a data inputsignal; modulating the data input signal; performing a direct sequencespread spectrum operation on the data input signal resulting in a spreaddata input signal; converting the spread data input signal to a spreadradio frequency data signal; amplifying the spread radio frequency datasignal with a first amplifier having an adjustable gain control;selectively amplifying the radio frequency data signal with a secondamplifier having an adjustable bias current control in accordance with adesired transmission output power, wherein selection of a lowertransmission power results in a lower current usage by the secondamplifier; selectively detecting a power signal from at least a portionof the radio frequency data signal and a printed circuit board couplerthat couples transmission power to a radio frequency detector diodecircuit; converting the at least a portion of the radio frequency datasignal to an analog error signal by a digital to analog converter;amplifying the radio frequency data signal proportionately with theerror signal by adjusting the gain control of the first amplifier toachieve a substantially constant output transmission power over aspecified temperature range; transmitting the radio frequency datasignal through by at least one antenna.

Another aspect of the invention is to maintain communications over abroad temperature range at a substantially constant output transmissionpower.

In another embodiment, the invention utilizes a digital feedback loop toadjust the output of the power amplifier to keep the output powerconstant over a typical temperature range.

In another embodiment, the invention may allow the user to select apredetermined transmit output power and lower the current drain whenmaximum output power is not required, thereby conserving battery lifewhen a lower output power transmission is required.

Still other advantages of the invention will become apparent to thoseskilled in the art upon a reading and understanding of the followingdetailed description, accompanying drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, a preferred embodiment and system and method of which will bedescribed in detail in this specification and illustrated in theaccompanying drawings which form a part hereof, and wherein:

FIG. 1 is the transmit spectrum mask described in IEEE 802.11;

FIG. 2 is a schematic representation of a typical WLAN configuration;

FIG. 3A is an exemplary representation of a building to buildingconfiguration of the present invention;

FIG. 3B is an exemplary representation of a building to buildingconfiguration of the present invention;

FIG. 4 is a schematic representation of an exemplary embodiment of atypical base station transmitter;

FIG. 5 is a schematic representation of the present invention;

FIGS. 6A-6C graphically illustrate the relationship between the diodedetector input power and diode detector output voltage over a range oftemperatures.

DETAILED DESCRIPTION OF THE INVENTION

It should be appreciated that a preferred embodiment of the presentinvention as described herein makes particular reference to the IEEE802.11 Standard, and utilizes terminology referenced therein. However,it should be understood that reference to the IEEE 802.11 standard andits respective terminology is not intended to limit the scope of thepresent invention. In this regard, the present invention is suitablyapplicable to a wide variety of other communication systems whichutilize a plurality of operating frequencies for data transmission.Moreover, it should be appreciated that while the present invention hasbeen described in connection with a wireless local area network (WLAN),the present invention is suitable for use in connection with other typesof wireless networks, including a wireless wide area network (WWAN), awireless metropolitan area network (WMAN) and a wireless personal areanetwork (WPAN).

Referring now to FIG. 2, there is shown a typical WLAN used with thepresent invention. More specifically, FIG. 2 shows a WLAN system 2generally comprised of a plurality of communication devices includingmobile stations (i.e., portable units 16, 20, 22, 24 and 26, andhand-held unit 18) and a plurality of base stations (also commonlyreferred to as access points or base stations) B0, B1, B2, and B3. Thebase stations may be connected to a hardwired network backbone or serveas wireless base stations. Each base station can transmit and receivedata in its respective cell. WLAN system 2 also includes a cable medium,namely, an Ethernet cable 10, along which all network data packets aretransmitted when conveyed between any two network nodes. The principalnodes are direct-wired to the cable 10. These include a work station 12and a network server 14, but may include a mainframe computer,communication channels, shared printers and various mass storage.

In WLAN system 2, base station B2 effectively operates as a repeater,coupled to the cable 10 by the base station B3 and a radio link with thebase station B3. Base station B2 has been termed a “base station”because it registers mobile stations in the same manner as the basestations that are direct-wired to the cable 10, and offers the samebasic registration services to the mobile stations. The base station B2and each device to which it offers packet transferring services will,however, be registered with the base station B3 to ensure that packetsintended for or transmitted by devices associated with the base stationB2 are properly directed through the base station B2.

Several LANs are present in the WLAN system 2. These LAN's are notspecifically indicated, but each is effectively defined by the areawhich a single base station can serve, given limited transmission power,and the devices within that area. One LAN is served by the base stationB0 and currently contains a portable unit 16, such as a line-poweredpersonal computer, and a battery-powered hand-held unit 18. A second LANis served by another base station B1 and currently contains two portableunits 20, 22. A third LAN is served by the other wired base station B3and also contains two portable units 24, 26. A fourth LAN is served bythe base station B2, and no network device is currently within the rangeof that base station. The cable 10 and its nodes are also treatedeffectively as a LAN. It should be noted that all transmission betweendevices in different LAN's is via the cable 10. Only transmissionsbetween devices in a single LAN avoid using the cable 10, but suchmatters are not discussed extensively herein.

General operation of the network to accommodate movement of thehand-held unit 18 will now be described. The hand-held unit 18 isassumed to be registered initially with the base station B0. The basestation B0 is also assumed to have undelivered packets addressed to thehand-held unit 18. The hand-held unit 18 is assumed then to move toposition A, illustrated in phantom outline in FIG. 2, assumed to bebeyond the transmission range of the base station B0. The hand-held unit18 transmits polling packets at intervals, following its power-savingroutine, with no response from the base station B0. After apredetermined number of attempts to poll the base station B0, thehand-held unit 18 causes transmission of a packet requestingregistration with a network communication base station and providing itsunique network address or identification. The registration-requestingpacket is assumed in this instance to be received only by the basestations B1 and B3.

It is assumed that both base stations B1 and B3 can accommodate anotherdevice. Each then transmits a response packet addressed to the hand-heldunit 18 and each reserves a registration slot for a predetermined periodof time. Each response packet will include the base station's uniquenetwork address and will also indicate the number of hops from the basestation to the cable 10. A base station connected directly to the cable10 is regarded as 0 hops from the cable 10. A base station thatfunctions as a repeater returns a positive number indicating the numberof intervening base stations (hops) required to couple it to the cable10.

The hand-held unit 18 then responds to the base station response packetsby selecting one of the responding base stations B1, B3. The selectionis made according to the number of hops to the cable 10, signal strength(detected in a conventional manner), and which response packet is firstreceived, priority being assigned in that order. In the present case,governed by the second criterion, namely, signal strength, and assumingthat the closer base station B1 produces a stronger received signal, thehand-held unit 18 selects the base station B1. The hand-held unit 18then transmits a selection packet addressed to the base station B1requesting registration. The selected base station B1 responds to theselection packet by registering the hand-held unit 18 and begins theprocess of monitoring the cable 10 for packets addressed to thehand-held unit 18. Base station B1 also recognizes and conveys to thecable 10 any data packets received from the hand-held unit 18. The basestation B3, not selected, but within range, does not respond to packetsin the cable 10 addressed to the hand-held unit 18 and does not respondto any data packets received from the hand-held unit 18. No duplicatepackets are produced within the cable 10 and no duplicate packets aretransmitted through air.

Contemporaneously with registration, the selected base station B1transmits via the cable 10 a multicast packet indicating itsregistration of the hand-held unit 18. The multicast packet contains aunique address for each of the network base stations. The multicastpacket is conveyed via the cable 10 to the base station B0 with whichthe hand-held unit 18 had been registered. The base station B0 respondsby immediately de-registering the hand-held unit 18, discontinuingmonitoring of the cable 10 for packets addressed to the hand-held unit18 and disregarding further packets of a general nature transmitted bythe hand-held unit 18 and possibly received by the base station B1. Thebase station B0 also responds by transmitting along the cable 10 anyundelivered packets that are addressed to the hand-held unit 18. Thenewly selected base station B1 retrieves the packets from the cable 10and stores them for re-transmission to the hand-held unit 18.

The hand-held unit 18 may then move to position B shown in phantom inFIG. 2. It is assumed now to be out of range of the base station B1 butstill within the range of base stations B3 and B2. After predeterminedattempts to contact the base station B1 with polling packets, thehand-held unit 18 sends a packet requesting registration with acommunication base station. It receives response packets only from thebase stations B2, B3. The packet from base station B2 will indicate thatthe base station B2 is one hop away from the cable 10, that is, the basestation functions as a repeater. The packet from the base station B3indicates direct connection to the cable 10 (zero hops). The hand-heldunit 18 consequently selects the base station B3 according to thecriteria specified above, and transmits a packet requesting registrationwith the base station B3. The base station B3 responds with responsepacket confirming registration, assuming no intervening registrationshave taken the full capacity of the base station B3. If the capacity ofthe base station were somehow taken, the hand-held unit 18 would repeattransmission of its selection packet, assume transmission failure, andre-initiate the process of locating an appropriate communication basestation. The base station B3 also transmits via the cable 10 a multicastpacket addressed to base stations indicating the registration, and thebase station B1 de-registers the hand-held unit 18. The base station B1transmits any undelivered packets addressed to the hand-held unit 18along the cable 10, and the new base station B3 detects and stores thepackets. In effect, the base station B3 is fully conditioned to continuepacket transmission from where the last base station lost communicationwith the hand-held unit 18

In position C illustrated in phantom in FIG. 1, the hand-held unit 18 isassumed to be out of range of all base stations except the base stationB2. With repeated failure in transmission of packets to the base stationB3, the hand-held unit 18 transmits a packet requesting registrationwith a base station. Only the base station B2 responds by transmittingan appropriate packet. The selection process at the hand-held unit 18 issimplified, the only criterion to be applied is that a base stationresponded and was effectively the first base station to respond. Thehand-held unit 18 then transmits its selection packet identifying thebase station B2 and requesting registration. The base station B2registers the hand-held unit 18, and transmits a multicast packet viathe cable 10 addressed to base stations confirming the registration. Thebase station B3 actually places the packet on the cable 10.

General operation of the representative WLAN network 2, as discussedabove, is known to those skilled in the art, and is more fully discussedin U.S. Pat. No. 5,276,680, which is fully incorporated herein byreference.

FIG. 3 illustrates another embodiment of the present invention. In FIG.3 a first base station 30 is located on the roof of a commercial orresidential building (Building A). Base stations 32 and 34 transmit andreceive data from the base station 30 (located on Buildings B and C,respectively). As shown in FIG. 4, base station 30 comprises anOmni-directional antenna 30 wired to a bridge 36A. The bridge 36A isconnected to an Ethernet cable 10A which supports networking throughoutthe commercial or residential building and permits the occupant ofBuilding A to receive and transmit data to and from Buildings B and C.Directional antennas 32 and 34 are similarly linked to bridges 36B and36C and the Ethernet cables 10B and C, respectively. Occupants ofBuildings B and C are able to transmit and receive data to and fromBuilding A. However, due to the use of directional antennas 32 and 34,occupants of Buildings B and C are not able to communicate directly witheach other. In order for such communication to occur, the data mustfirst be sent to Building A and then routed to the appropriate building.

As can be readily appreciated by those of ordinary skill in the art,increasing the effective communication range of the mobile units and thebase stations will generally result in less network resources beingwasted in establishing communications between base stations.Accordingly, WLAN devices which are capable of increased transmissionranges will generally be more efficient than those WLAN devices having asmaller transmission range. In addition, the increased transmissionrange may decrease consumer costs associated with WLAN devices becausethe quantity of base stations to appropriately cover a geographical areamay be less than those base stations with a more limited transmissionrange.

FIG. 4 shows an exemplary embodiment of a wireless radio transmitter.Typically, multiple integrated circuits are combined to implement a datacommunications radio 40. The primary components of the radio, from thePCMCIA connector 42, are as follows: the media access controller 44, thedirect sequence spread spectrum baseband processor or PHY chip 46, theI/Q modulator/demodulator and synthesizer 48, the RF-to-IF converter 50,the power amplifier and detector 52, and the antennas 54A and 54B. Onemanufacturer that manufactures and sells a corresponding integratedcircuit for each of the function blocks listed in FIG. 4 is IntersilCorporation of Mountaintop, Pa. For example, the Intersil PRISM II® chipset consists of the following integrated circuits: the HFA3842 mediaaccess controller, the HFA3863 baseband processor, the HFA3 783 I/QModulator/demodulator, the HFA3683A RF/IF converter, and the HFA3983power amplifier.

An embodiment of the present invention incorporates certain PRISM II®integrated circuits. However, one of ordinary skill in the art shouldreadily appreciate that the present invention is not limited to thePRISM II® chip set.

FIG. 5 illustrates an embodiment of the present invention. The generaloperation of the radio 60 will now be described. On the transmit side, adata signal is received from the PCMCIA connector 62 to the media accesscontroller (“MAC”) 64. Presently, the MAC 64 is a media accesscontroller Part No. 08-0458-01, manufactured by Cisco Systems, Inc. ofSan Jose, Calif. The MAC 64 contains the following functionality: aPCMCIA interface control 90, a memory interface control 92, receivefunctions 94, and transmit functions 96. In addition, the MAC 64 islinked to a static random access memory 98, a flash memory 100, a 32 kHzoscillator 102 and a 44 MHz oscillator 104.

The signal received from the PCMCIA connector 62 is received by thetransmit function block 96 and routed to the baseband processor (“PHY”)66. Presently, the PHY 66 is Part No. HFA3863, manufactured by Intersilof Mountaintop, Pa. The PHY 66 is comprised of two functional blocks, adespread function 106 and a spread function 108 depending on whether thesignal is being received or transmitted. The signal routed to the PHY 66is directed to the spread function 108. The spread function 108 performsa direct sequence spread spectrum operation on the signal. For example,a binary phase shift keyed (“BPSK”) operation, complimentary code keyed(“CCK”) or a quadrature phase shifted keyed (“QPSK”) operation isperformed.

Operation of the spread function 108 results in the baseband “I” and “Q”signals being determined for the input data signal. The “I” and “Q”signals are then transmitted to the I/Q MODEM 68. In the presentinvention, the I/Q modulator/demodulator is Part No. HFA3783,manufactured by Intersil. The I/Q MODEM 68 is composed of the followingfunctional elements: an I/Q demodulator 110, an I/Q modulator 112, atransmit variable gain amplifier 114, and a phase lock loop circuit 116.In addition, the phase lock loop circuit is connected to an externalvoltage controlled oscillator 118. The “I” and “Q” signals transmittedfrom the PHY 66 are sent to the I/Q modulator 112 which converts thebaseband spread spectrum signal to an intermediate frequency (“IF”) ofapproximately 374 MHz.

The IF signal is then sent to the saw filter 70. The saw filtered signalis then sent to the RF/IF converter 72. Presently, the RF/IF converter72 is Part No. HFA3683A manufactured by Intersil. The RF/IF converter iscomposed of the following functional elements: a phase lock loop circuit120, an oscillator buffer amplifier 122, mixers 124 and 126, a receivehigh pass filter 128, a transmit bandpass filter 130, a receive variablegain low noise amplifier 132, and a transmit driver amplifier 134. Inaddition, the phase lock loop circuit 120 is connected to a radiofrequency voltage controlled oscillator 136. The signal routed from thesaw bandpass filter 70 is sent to the mixer 126 where the signal ismixed (up converted) with an oscillator generated frequency of 2,068 MHzoriginating from the radio frequency voltage controlled oscillator 136.The resulting signal frequency is approximately 2,450 MHz (or 2.4 GHz)and places the signal to be transmitted in the 2.4-2.483 GHz IndustrialScientific Medical (“ISM”) band of the radio spectrum.

The mixed signal is then sent to the transmit bandpass filter 130 andthe transmit driver amplifier 134 and exits the RF/IF converter 72. Thesignal is filtered through bandpass filter 74, amplified by poweramplifier 76, routed to the transmit/receive switch 78, filtered throughlow pass filter 80, through an antenna switch 82, low pass filtered byeither filters 84A or 84B and transmitted out the spatially diverseantennas 86A and 86B. Note, FIG. 5 also shows the low noise amplifier 75and the receive bandpass filter 77. Amplifier 75 and filter 77 areassociated with the receive portion of the radio 60.

Presently, the power amplifier 76 is Part No. RMP2451-53 manufactured byRaytheon Semiconductor Co. from Mountain View, Calif. Output from thepower amplifier 76 is also directed to the printed circuit board coupler138 and routed to a diode power detector 140. In the preferredembodiment, the printed circuit board coupler 138 is a printed circuitboard microstrip coupler that couples power to the diode power detector140. In addition, the diode power detector 140 is a zero bias schottkydiode. A zero bias schottky diode characteristically has little driftover temperature when operated at high input power levels. Thus, in thepreferred embodiment a −17 dB printed circuit board microstrip couplercouples relatively high input power levels to the Schottky diode. Thisresults in a detector transfer function that has only a small amount ofdrift over a broad temperature range.

From the diode power detector 140, an analog voltage is sent to the PHY66. The PHY 66 accepts the analog signal, typically in the range of0-1.5 Volts. The signal is converted by an analog to digital converter144 and routed to a digital comparison function 148. A digital referenceword 150 corresponding to the desired output power is compared to theconverted digital signal. Through the transmit automatic gain controlfunction of the PHY 66, a corresponding error signal is produced. Theerror signal is converted to an analog signal by the digital to analogconverter 146 and routed to the variable gain amplifier 114 of the ofthe I/Q MODEM 68. The error signal effectively provides a digitalfeedback control loop between the transmitted signal and the next signalto be transmitted, thereby the output power of the radio 60 iseffectively held constant. This digital feedback loop enables monitoringof the transmitted signal and the ability to increase or decrease thegain of amplifier 114 in order to output a constant power over a widerange of temperatures.

The power amplifier 76 is a monolithic microwave integrated circuitpower amplifier that has a current bias control function. Presently, thebias select of the power amplifier 76 is adjusted by a digital to analogconverter 142 to set a desired bias current for each transmit outputpower. In the present embodiment, the DAC 142 is programmed by a threewire bus and enables adjusting the bias select in 1/256 increments.

The present invention currently supports six predetermined powertransmission output levels: 1 mW, 5 mW, 20 mW, 30 mW, 50 mW, and 100 mW.Currently, the digital feedback loop discussed above is available onlyfor the 20 mW and higher transmission powers. One advantage of the poweramplifier 76 is that the transmit current drain may be lowered when theradio is transmitting at less than its maximum output range, in thiscase 100 mW. Thus, at output transmission powers of less than 100 mW,the present invention utilizes DAC 142 to set a lower transmit currentdrain which lengthens the battery life of the radio 60. For the loweroutput transmission powers, i.e., 1 mW and 5 mW, the amplifier gains arepre-selected and may be manually altered.

FIGS. 6A-C illustrate typical diode detector input power and outputvoltage curves at 2400 MHz, 2450 MHz, and 2500 MHz, respectively, whilethe temperature is varied between 30 degrees Celsius and 70 degreesCelsius. The term “substantially” as used in the claims to refer to“substantially constant output transmission power over a temperaturerange” shall be defined with reference to FIGS. 6A-6C.

The invention has been described with reference to a preferredembodiment. Obviously, modifications and alterations will occur toothers upon a reading and understanding of this specification. It isintended that all such modifications and alterations be included insofaras they come within the scope of the appended claims or the equivalentsthereof.

Having thus described the invention, it is now claimed:
 1. A method fortransmitting data communications through air using a radio comprising:receiving a data input signal; modulating the data input signal;performing a direct sequence spread spectrum operation on the data inputsignal resulting in a spread data input signal; converting the spreaddata input signal to a spread radio frequency data signal; amplifyingthe spread radio frequency data signal with a first amplifier having anadjustable gain control; selectively amplifying the radio frequency datasignal with a second amplifier having an adjustable bias current controlin accordance with a desired transmission output power, whereinselection of a lower transmission power results in a lower current usageby the second amplifier; selectively detecting a power signal from atleast a portion of the radio frequency data signal and a printed circuitboard coupler that couples transmission power to a radio frequencydetector diode circuit; converting the at least a portion of the radiofrequency data signal to an analog error signal by a digital to analogconverter; amplifying the radio frequency data signal proportionatelywith the error signal by adjusting the gain control of the firstamplifier to achieve a substantially constant output transmission powerover a specified temperature range; transmitting the radio frequencydata signal through by at least one antenna.
 2. A method according toclaim 1, wherein selection of the desired transmission output power isaccomplished by inputting the desired transmission output level into adigital to analog converter connected to the adjustable gain control ofthe first amplifier.
 3. A method according to claim 1, wherein saiddirect sequence spread spectrum operation consists of either a binaryphase shift key operation, complimentary code keyed or a quadraturephase shift key operation.
 4. A method according to claim 1, whereinsaid step of selectively generating an error signal includes the step ofdetecting a power signal by a zero bias schottky diode.
 5. A methodaccording to claim 1, wherein said step of selectively generating errorsignals includes the step of generating at least a portion of the powersignals from the printed circuit board coupler wherein the printedcircuit board coupler is a printed circuit board microstrip coupler. 6.A method according to claim 1, wherein the step of amplifying the radiofrequency data signal proportionately includes the step of controllingthe first amplifier gain to achieve a substantially constant outputtransmission power over a temperature range varying from −30 degrees to70 degrees Celsius.
 7. A method according to claim 1, wherein the stepof amplifying the radio frequency data signal proportionately includesthe step of generating the output transmission power to be no greaterthan 100 mW.
 8. An apparatus for transmitting data communicationsthrough air using a radio comprising: a receive means adapted forreceiving an associated data input signal; a modulating means adaptedfor modulating the associated data input signal; a spreading means forperforming a direct sequence spread spectrum operation on the associateddata input signal resulting in a spread data input signal; a convertingmeans for converting the spread data input signal to a spread radiofrequency data signal; an amplifying means for amplifying the spreadradio frequency data signal with a first amplifier having an adjustablegain control; an amplifying means for amplifying the spread radiofrequency data signal with a second amplifier having an adjustable biascurrent control for selecting a bias current for a desired transmissionoutput power wherein selection of a lower transmission power results ina lower current drain; a detecting means for detecting a power signalcreated from at least a portion of the radio frequency data signal; acoupler means for coupling transmission power to a radio frequencydetector diode circuit; a converting means for converting for convertingthe at least a portion of the radio frequency data signal to an analogerror signal; an amplifying means for amplifying the radio frequencydata signal proportionately with the error signal by adjusting the gaincontrol of the first amplifier to achieve a substantially constantoutput transmission power over a selected temperature range; and atransmission means adapted for transmitting the radio frequency datasignal through at least one associated antenna.
 9. An apparatusaccording to claim 8, wherein the adjustable gain control is selected bya digital to analog converter connected to the adjustable gain controlof the first amplifier which corresponds to the desired transmissionoutput power.
 10. An apparatus according to claim 8, wherein saidspreading means consists of either a binary phase shift key operation,complimentary code keyed, or a quadrature phase shift key operation. 11.An apparatus according to claim 8, wherein said detecting means fordetecting a power signal is performed by a zero bias schottky diode. 12.An apparatus according to claim 8, wherein said coupler means is aprinted circuit board microstrip coupler.
 13. An apparatus according toclaim 8, wherein the output transmission power is substantially constantover a temperature range varying from −30 degrees to 70 degrees Celsius.14. An apparatus according to claim 8, wherein the output transmissionpower is no greater than 100 mW.